Forming an aluminum casting with a bronze insert



April 14, 1959 H. L. BENHAM FORMING AN ALUMINUM CASTING WITH A BRONZE INSERT Filed June 9, 1958 ATTORNEY United States Patent FORMING AN ALUMINUM CASTING WITH A BRONZE INSERT Harold L. Benliam, Bedfortl, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware application May 24, 1956, Serial No. 587,152. and this application June 9, 1958, Serial No.

4 Claims. (Cl. 22203) This invention relates to a method of forming an aluminum or aluminum alloy casting having a copper base alloy insert and particularly to a process for making a thrust bearing of these components. The present application is a division of patent application Serial No. 587,152, which was filed on May 24, 1956.

In the manufacture of journal-bearing assemblies for railway freight and passenger cars and the like it has become desirable to use aluminum alloy sleeve bearings in conjunction with steel journals or journal sleeves. Sealed-cartridge journal bearings of this type are shown in co-pending patent applications Serial Nos. 529,625 and 566,460, filed August 22, 1955 and February 20, 1956, respectively, in the name of Earl J. Clark.

The aluminum alloy bearing in this form of journalbearing assembly functions as a thrust bearing as well as a sleeve bearing. In some modifications of this assembly the thrust bearing surface provided by the aluminum alloy is entirely satisfactory because of excellent lubrication, while in others this surface wears at an excessive rate. Under the latter circumstances it is desirable to provide a long-wearing bronze insert in the end of the aluminum alloy bearing sleeve.

However, in manufacturing this hearing, if the aluminum base alloy is cast directly against the bronze insert, one or more low-melting point alloys are formed with an attendant reduction in the volume of the two metals. It was found, for example, that when the molten aluminum contacts the bronze, zinc and/ or various other constituents in the bronze diffuse into the aluminum and form a eutectic mixture such as aluminum-zinc. The lower melting point constituents in the bronze actually migrate to and alloy with the aluminum base metal. These constituents, such as lead, zinc, etc., are frequently essential to provide the bronze insert with desirable bearing properties, and if they alloy with the aluminum the effectiveness of the insert is substantially reduced.

It is believed that the copper in the bronze and the aluminum also form a relatively low melting point alloy. This absorption or diffusion into the aluminum of the copper or other constituents in the bronze produces shrink cavities in the aluminum alloy at the interface of the insert and the aluminum alloy. These shrink cavities or worm holes are formed because the aluminum solidifies against the insert before the aforementioned diffusion is complete, thus entrapping the lower melting point alloy or alloys which subsequently shrink. In other words, when the metallic constituents in the bronze hearing migrate into the aluminum they are entrapped in the solidifying aluminum. When a lower melting point eutectic subsequently freezes, it shrinks because of lack .of proper feeding, thus producing the shrink cavities.

Also, since the type of bearing referred to above operates at a temperature of approximately 400 F. to 500 R, an aluminum bearing containing the aforementioned aluminum-zinc component would partially melt under operating conditions. Hence it is necessary to prevent the formation of this and other undesirable low-melting point eutectics in the bearing.

Accordingly, a principal object of the present invention is to provide a method of casting aluminum or aluminum alloy into contact with a copper base alloy so that there is no migration or diffusion of the constituents in the copper base alloy into the aluminum. A further object of this invention is to provide a process for casting aluminum or an aluminum alloy against a bronze insert in a manner which prevents the aforementioned de-zinification of bronze or formation of other undesirable lowmelting eutectics. A still further object of the invention is to provide a thrust bearing produced by casting aluminum around a bronze insert in such a manner that alloying of the two metals is substantially eliminated and in which the insert is mechanically locked in position in the aluminum casting.

These and other objects are attained in accordance with the present invention by the use of a copper oxide barrier layer between the bronze insert and the aluminum alloy. Specifically, a black copper oxide coating is formed on the surfaces of the bronze by heating the insert to the red-hot temperature range before casting the aluminum around it. As a result, practically no alloying occurs between the bronze and the aluminum base alloy, yet a mechanical bond retains the two metals in close surface contact.

Other objects and advantages of this invention will more fully appear from the following detailed description thereof, reference being made to the accompanying drawing in which:

Figure 1 is a longitudinal sectional view of a portion of a journal-bearing assembly embodying the present invention;

Figure 2 is a longitudinal sectional view of a portion of a modification of the journal-bearing assembly shown in Figure l; and

Figure 3 is an enlarged sectional view of the ring-shaped bronze insert shown in Figures 1 and 2.

Referring more particularly to the drawing, in Figure l is shown part of a sealed-cartridge journal-bearing assembly for railway freight and passenger cars. An axle 10 having a journal portion 12 is shown rotatably supported within an aluminum alloy sleeve bearing 14. If desired, the bearing surface of this sleeve may be provided with a thin overlay 15 of a suitable lead base alloy, such as lead-tin or lead-indium. A housing 16 surrounds the journal-bearing assembly and is provided with a portion 18 at its inner end forming a support for an annular oil seal 20.

As shown in Figure 1, the outer periphery of the oil seal contacts the housing and the inner periphery contacts a hardened thrust ring 22 secured to the axle by a shrink fit. This thrust ring is shaped so as to have portions 24 and 26 contacting the journal and to leave a space 28 between the thrust ring and a portion of the journal. The thrust ring may be formed of suitable hard wear-resistant material such as carbonitrided and hardened steel. Adjacent the thrust ring and bronze insert there is provided an annular groove 29 in the housing to permit return of excess oil to an oil reservoir, not shown, in the lower portion of the housing.

The axle journal 12 is provided with a seamless hardened journal sleeve 30 which is shrink fitted around the journal or attached thereto by other appropriate means. This journal sleeve may be made of any suitable wearresistant metal, such as steel having its outer surface carbonitrided and hardened. During operation this sleeve is, in effect, a portion of the rotating journal, but it may be readily replaced should excessive wear or scoring OCCHI The end face 32 of the thrust ring 22 is normally spaced at 34 from the end of the sleeve bearing 14 as illustrated in Figure 1. However, when the railway car is traveling around a curve or otherwise when there are forces causing relative axial movement between the journal and bearing, this space 34 will close and the adjacent end of the bearing sleeve will contact the end face of the thrust ring. Under these circumstances, excessive wear of the end of the aluminum alloy bearing sleeve may occur, particularly if not thoroughly lubricated, unless it is provided with a more wear-resistant surface. Accordingly, a bronze insert 38 is located at the flanged end 40 of the bearing sleeve.

This bronze insert is ring shaped and is provided with a plurality of circumferentially spaced openings 42. In forming the bearing sleeve 14 the aluminum alloy is cast against this annular insert so that the molten aluminum alloy flows into the openings 42 to form locking fingers 46 which rigidly hold the insert in position against the flanged end 40 of the bearing sleeve casting. Either during the casting process or by subsequent machining it is preferable to form the fingers 46 so that they are slightly recessed axially and do not contact the end face 32 of the thrust ring 22. In this manner the bronze insert is the only portion of the bearing which functions as a thrust surface. It will also be noted that the openings 42 in the bronze insert ring 38 are tapered at 44 so that the aluminum locking portions 46 are flared radially outward at their outer ends 48 to prevent axial movement of the insert relative to the aluminum bearing sleeve.

In the modification of the invention shown in Figure 2 the oil seal is omitted. With this arrangement it is particularly desirable to employ the annular bronze insert 38 at the thrust bearing end of the aluminum alloy sleeve 30. Otherwise this end of the sleeve would be subject to rapid wear and galling due to inadequate lubrication and the presence of foreign particles in the space 34 between the thrust ring 22 and the bearing sleeve. Even when the thrust bearing surface is very poorly lubricated, the bronze insert will not gall.

The annular bronze insert 38 may be formed of any copper base alloy suitable for thrust bearing applications. Hence the term bronze is intended to include various alloys containing at least 50% copper and minor amounts of other metals. Among the alloying constituents which may be used are tin, zinc, nickel, lead, manganese, aluminum, silicon, arsenic, antimony and phosphorus. Normally the bronze should not contain more than about 20% tin or 30% zinc. Since nickel is completely miscible in copper, it also may be present in appreciable amounts but preferably not in excess of approximately 20%. Such a bronze will usually contain about 1% to silicon and not in excess of 1% phosphorus. Usually the manganese and lead contents of the bronze should not exceed approximately 5% and 3%, respectively. A preferred bronze composition for use in the abovedescribed thrust bearing application is one consisting essentially of zinc, 0.05% lead, 0.05% iron and the balance substantially all copper.

After the openings 42 have been drilled or otherwise formed in the bronze insert 38 the surfaces of the insert are provided with a copper oxide barrier layer 50 which prevents the aforementioned undesirable alloying of the bronze with the aluminum. Such a barrier layer precludes metal constituents in the bronze from alloying with the molten aluminum at the interface of the two metals during castings of the aluminum alloy. The copper oxide layer may be formed by heating the bronze insert to a temperature of 1000 F. to 1400 F. over an open flame. A temperature between 1200 F. and 1400 F. is preferably employed. This heating, which brings the temperature of the bronze insert into the red-hot range, provides the insert with a coating or film of black copper oxide due to the oxidation of the copper in the bronze.

The black copper oxide barrier layer provided is extremely thin, generally not in excess of approximately 0.001 inch in thickness. This copper oxide is the mono oxide, CuO, which is produced by the rapid oxidation due to the flame treatment.

Thereafter the bronze insert is placed in a die which is preferably formed of cast iron or sheet steel. This may advantageously be done while the insert is still hot. Next the molten aluminum alloy is poured around the bronze insert, preferably at a pouring temperature of about 1250" F. to 1450 F. The molten aluminum alloy flows into the casting cavity and the openings 42 in the bronze ring, thereby forming the locking fingers 44. Upon solidification of the aluminum base alloy casting, these fingers securely retain the ring against the surfaces of the casting.

Among the aluminum base alloys which may be used to form the bearing sleeve 14, excellent results have been obtained with the alloy described in United States Letters Patent No. 2,238,399 in the name of Alfred W. Schluchter. Hence an aluminum base bearing alloy consisting essentially of 0.05 to 5% cadmium, 0.3% to 11% silicon and the balance aluminum is satisfactory. A somewhat harder and stronger aluminum alloy bearing which may be employed is described and claimed in copending patent application Serial No. 250,191, filed on October 6, 1951 now Patent No. 2,766,116, in the name of Alfred W. Schluchter. Thus the aforementioned aluminum base alloy may be further improved for some applications by the presence of 0.05 to 3% magnesium and/or 0.1% to 2.25% chromium. In all instances, however, it is desirable to use an alloy containing at least aluminum.

Not only does the CuO film function as a barrier to prevent the low-melting metal constituents in the bronze from alloying with the molten aluminum, but it also affords several other advantages. The hot copper oxide coating permits the aluminum alloy to closely contact the bronze insert on cooling. Moreover, since the molten aluminum alloy may be poured around the bronze insert while the latter is still hot, blows will not be produced in the aluminum alloy nor will it be chilled during the casting operation. I

As a result of the above-described process, the bronze insert is mechanically locked in place, and no metallic bonding occurs between it and the aluminum casting. It is believed that the bronze and aluminum alloy do not actually touch and that the only contact is between the CuO barrier layer and the aluminum alloy. For all practical purposes the CuO is insoluble in the aluminum alloy because of the short contact time between the molten aluminum and the bronze and the relatively low casting temperature of the aluminum alloy.

While this invention has been described by means of certain specific examples, it will be understood that the scope of the invention is not to be limited thereby except as defined in the following claims.

I claim:

1. A method of forminga composite article of a copper base alloy and an aluminum alloy, said method comprising heating a copper base alloy member to a temperature suflicient to form a thin coating of CuO on the surface of said member, placing said member in a die, thereafter pouring molten aluminum base alloy into contact with said coated member and permitting said aluminum base alloy to solidify.

2. A method of forming a composite article which comprises heating a bronze member to a temperature between approximately 1000 F. and 1400 F. to thereby form a thin layer of CuO on surfaces of said member, subsequently placing said member while still hot in a mold, and thereafter pouring molten aluminum base alloy into said mold so that said molten aluminum base alloy contacts said CuO layer and mechanically secures said bronze member to said aluminum base alloy on solidification thereof.

3. A method of forming a composite hearing which comprises forming a hole in a zinc-containing copper base alloy member, thereafter flame heating said member to a temperature between approximately 1200" F. and 1400 F. to thereby form a coating of CuO having a thickness not in excess of approximately 0.001 inch on the surfaces of said member, placing said coated member in a metal mold having a casting cavity formed in the shape of a bearing, subsequently pouring molten aluminum base alloy at a temperature between 1250 F. and 1450 F. into said casting cavity so that said molten aluminum base alloy contacts said CuO coating and a portion thereof flows into said opening, and finally permitting said aluminum base alloy to solidify and securely lock said copper base alloy to said aluminum base alloy casting.

4. A method of forming a composite bearing which comprises forming a hole in a zinc-containing copper base alloy member, heating said member in an open flame to a temperature between approximately 1000 F. and 1400 F. to thereby form a thin layer of CuO on surfaces of said member, subsequently placing said member while still hot in a mold, thereafter pouring molten aluminum base alloy into said mold so that said molten aluminum base alloy contacts said CuO, permitting said aluminum base alloy casting to solidify and thereby secure said copper base alloy member to said casting, and finally coating bearing surfaces of said aluminum base alloy casting with a thin overlay of a soft bearing metal selected from the class consisting of lead and lead base alloys.

References Cited in the file of this patent UNITED STATES PATENTS 1,926,320 Trembour Sept. 12, 1933 2,330,757 Stout Sept. 28, 1943 FOREIGN PATENTS 407,120 Great Britain Oct. 7, 1932 

1. A METHOD OF FORMING A COMPOSITE ARTICLE OF A COPPER BASE ALLOY AND AN ALUMINUM ALLOY, SAID METHOD COMPRISING HEATING A COPPER BASE ALLOY MEMBER TO A TEMPERATURE SUFFICIENT TO FORM A THIN COATING OF CUO ON THE SURFACE OF SAID MEMBER, PLACING SAID MEMBER IN A DIE, THEREAFTER POURING MOLTEN ALUMINUM BASE ALLOY INTO CONTACT WITH SAID COATED MEMBER AND PERMITTING SAID ALUMINUM BASE ALLOY TO SOLIDIFY. 